This male fisher was found dead near Yosemite National Park. Tissue samples confirmed the animal was killed by rat poison.

Elizabeth Shogren
/ NPR

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Originally published on February 14, 2014 7:58 pm

People who grow marijuana illegally in the backwoods of Northern California use large amounts of rat bait to protect their plants — and these chemicals are killing several species of wild animals, including rare ones, biologists say.

Here's what happens: The growers plant their marijuana in remote locations, hoping to elude detection. They irrigate their plants — with water from streams — which lures animals looking for water. Rodents chew the flourishing plants to get moisture, which kills the plants. Researchers believe that's the prime reason growers use the poisons.

"The problem is we have wild rodents out here that are going to eat the rat poisons, and then they become little time bombs," says Mark Higley, wildlife biologist in the area for the Hoopa Valley Tribe. "They don't die for seven to 10 days, maybe two weeks. And they stagger around and then become easy prey for Northern spotted owls, fishers, foxes, bobcats."

In studies of fishers (a rare relative of the weasel), nearly all the tracked animals that died in recent years — from the southern Sierra to the northern tip of the state — had rat poison in samples of their tissue.

And on the Hoopa reservation alone, postmortem exams have shown that rat bait caused nearly a third of the deaths of male fishers in recent years.

"To know that such a high percentage of the fisher population across the entire range in California was exposed to these rat poisons — and knowing that it's not just fishers, but all the other carnivores that have got to be exposed — it just seems absolutely criminal," says Higley.

One winter day, Higley, some of his fellow researchers and I scramble through a snow-covered wilderness. On a remote hillside, Higley finds a withered plant.

"Here's a marijuana plant that kept growing after it was cut," he says.

It's part of the remains from a raid last summer. A law enforcement team swooped in by helicopter and found 8,000 marijuana plants here, all between 3 feet and 6 feet tall, as well as lots of leftover rat poison and empty poison containers — trash left by the growers. (Most of the plants were hauled away, but some of the poison got left behind.)

Higley says this has become a common scene in the tribe's forests and throughout Northern California.

Sometimes the growers' poisons seem intended not for rodents, but for bigger animals. In another bust last summer, for example, in a national forest near the reservation, sheriff's deputies found a dead fisher. Above it, hot dogs laced with a toxic insecticide hung on large fish hooks.

The fisher had chunks of hot dog in its esophagus and stomach; it died of acute poisoning, says Higley, who accompanied law enforcement on that bust.

He and other biologists have a good sense of how these poisons are affecting fishers, because they've been studying the cat-size animals closely — the federal government has been considering putting fishers on the endangered species list. So biologists have been documenting their numbers and keeping track of how each animal dies. Researchers track each fisher with a radio collar; when an animal stops moving, they race into the forest to find its body before a predator does.

In fact, it was a dead fisher that first clued scientists into the widespread use of poisons by illegal pot growers. Blood had pooled in the animal's abdomen, a telltale sign of poisoning with anticoagulant rat bait.

At first the researchers were puzzled; fishers tend to live in remote areas, far from human homes. But once they learned of the poison used by illegal pot farmers, the scientists looked back through their collection of tissue samples from fishers that had died in previous years. Nearly all those samples, they discovered, contained traces of various rat poisons.

"It was just devastating," Higley recalls.

Since then, Higley has documented 19 illegal pot farms in the forests on the Hoopa reservation. He says the use of these dangerous chemicals on the reservation is particularly galling because the Hoopa Valley tribe banned all toxic chemicals decades ago to protect natural resources.

Pole has also helped clean sites after busts. He's seen how growers encircle their marijuana plants with rat poison and use large amounts of insecticide and fertilizer.

On the day of our visit, a big pile of trash remains from a cleanup a couple months earlier. It includes empty fertilizer bags and lots of irrigation hose the growers used to bring water from a stream. The area is so remote that a helicopter will be needed to come pick up the remaining mess — but funds for cleanups are hard to come by.

Only seven of the 19 known marijuana farms on the reservation have been cleaned up so far, according to Higley.

"It's pretty selfish," says Pole. "They come in. They reap the benefit of, you know, some quick cash. And all the environmental damage is happening here and we have to deal with it."

The fishers are a special concern to the tribe, whose members use fisher skins as arrow quivers in a traditional healing dance. But the tribe also worries about poisons getting into fish and game — and into the rivers where children play.

Wildlife ecologist Mourad Gabriel, of the nonprofit Integral Ecology Research Center, has been tracking the problem all over the northern half of California. In his lab in a logging town near the coast, he opens a locked freezer and pulls out the corpse of a furry animal.

"So you can see here, it's still a little frosty," he says, "but this is a beautiful, beautiful male fisher."

The animal was found dead near Yosemite National Park, several hundred miles from the Hoopa reservation. Gabriel tells me he'll take it to the University of California, Davis, for an examination to determine the cause of death.

Afterward, the scientists hike back into these spots and haul out whatever rat poisons they can find.

Gabriel sets up motion-sensing cameras to see which animals visit these sites and are, potentially, exposed to the poisons. The wildlife his photos have caught includes fishers, mountain lions, gray fox, deer and bears rummaging through trash piles — bottles of insecticide, fertilizer and other dangers.

Soon after my visit, Gabriel got back results from the autopsy of that frozen fisher. It did die from consuming rat poison (or a poisoned rat or other small animal).

And earlier this month, Gabriel suffered a very personal blow — his pet dog was poisoned with the same kind of rat bait and died. Gabriel thinks the poisoning was malicious. The local sheriff is investigating.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

ROBERT SIEGEL, HOST:

People who grow marijuana illegally in the backwoods of California are poisoning wild animals, including rare ones. They use rat bait and other toxic chemicals to protect their plants. NPR's Elizabeth Shogren visited the Hoopa Reservation in Northern California, where tribal members and biologists are worried about the problem.

ELIZABETH SHOGREN, BYLINE: We scramble through snow-covered brush on a remote hillside.

MARK HIGLEY: Here's a marijuana plant that kept growing after it was cut.

SHOGREN: The tribe's biologist, Mark Higley, holds up a rotten pot plant. It's left over from a bust last summer. A law enforcement team found 8,000 marijuana plants here, three to six-feet tall. They also found lots of rat poisons and empty containers left over after growers used the toxic chemicals. Here's what happens. The growers irrigate their plants. Rats chew on the plants to get moisture and that kills the plants. So the growers try to kill the rats.

HIGLEY: The problem is we have wild rodents out here that eat the rat poisons, and then they become little time bombs. They don't die for seven to 10 days, maybe two weeks, and they stagger around and then they become easy prey for northern spotted owl, fisher, foxes, bobcats.

SHOGREN: And then when predators eat the poisoned rodents, they get poisoned and sometimes die. Higley says this has become a common scene in forests throughout Northern California. That same week in a bust in a national forest nearby, sheriff's deputies found a dead fisher. It's a rare relative of the weasel, about the size of a cat. Higley was there. He says the marijuana growers had laced hotdogs with a toxic insecticide and hung them up on large fishhooks.

HIGLEY: And then that fisher had hotdog in its esophagus and in its stomach and died of acute poisoning.

SHOGREN: Higley and other biologists study fishers closely because the federal government is considering putting them on the endangered species list. They know what kills them because they tracked them with radio collars. When an animal stops moving, researchers race into the forest to find the body before predators do.

In fact, the dead fisher first clued in scientists for the widespread use of these poisons by illegal pot growers. Then researchers went back and looked at tissue samples from fishers that had died in previous years. Nearly all the animals had been exposed to rat poisons. Higley says these poisons cause nearly a third of the deaths of male fishers on the Hoopa Reservation over recent years.

HIGLEY: It was just devastating, I mean, to know that such a high percentage of the fisher population across the entire range in California was exposed to these rat poisons and knowing that it's not just fishers, but all the other carnivores got to be exposed to it. It just seems absolutely criminal.

SHOGREN: Particularly on the reservation. The Hoopa tribe banned all toxic chemicals decades ago to protect its natural resources. Aaron Pole is a wildlife technician and a member of the tribe.

AARON POLE: I'm enraged. Why won't they go somewhere else and grow?

SHOGREN: Pole has come across illegal marijuana farms when tracking fishers and rare northern spotted owls. And he's been part of teams cleaning up sites after busts. A big pile of trash is still left over from a clean up here a couple of months ago. It includes empty fertilizer bags and lots of irrigation hose that growers used to bring water from a stream.

POLE: It's pretty selfish. You know, it's like they come in and they're reaping the benefit of, you know, some quick cash. All the environmental damage is happening here and we have to deal with it.

SHOGREN: The fishers are a special concern because the tribe uses their skins for arrow quivers in a traditional healing dance. The tribe also worries about poisons getting into fish and game and the rivers where children play. Wildlife ecologist Mourad Gabriel is tracking the problem all over the northern half of California. In his lab in a logging town near the coast, he opens a locked freezer and pulls out a corpse of a furry animal.

MOURAD GABRIEL: So you can see here, it's still a little frosty but this is a beautiful, beautiful male fisher.

SHOGREN: It was found dead near Yosemite National Park hundreds of miles away. Gabriel plans to take it to the University of California, Davis for an examination to determine the cause of death. But these days, whenever a fisher turns up, he suspects rat poisons. He goes in with law enforcement during busts of illegal pot farms, sometimes getting lowered from a helicopter. Afterwards, he hikes back into the spots. He hauls out whatever rat poisons he finds and he sets up motion-sensing cameras.

GABRIEL: Just to see what kind of wildlife actually visits these sites.

GABRIEL: This bear is actually walking in and investigating bottles of insecticides and fertilizer.

SHOGREN: Gabriel recently got the results from the exam of that frozen fisher from Yosemite. It did die from rat poisons. And then earlier this month, Gabriel suffered a very personal blow. His pet dog was poisoned with the same kind of rat bait and died. He thinks it was malicious. The local sheriff is investigating. Elizabeth Shogren, NPR News.